The antinociceptive effect of intranigral injection of morphine in ketamine- and halothane-anesthetized rats.
Previous studies have shown that morphine, injected into the substantia nigra of rats, had an antinociceptive effect on the tail-flick test. However, due to a transient behavioral stimulant effect of morphine, given intranigrally, valid tail-flick latencies cannot be obtained prior to 30 min after the injection into the nigra. In order to examine the effect of morphine (5-20 micrograms), injected into the nigra, on the nociceptive tail-flick reflex at earlier times, animals were anesthetized with either halothane or ketamine (100 or 150 mg/kg, i.m.). Halothane blocked the analgesic effect of intranigrally administered morphine. However, a dose-related antinociceptive effect of morphine was observed in ketamine-anesthetized rats. This effect was demonstrable at 5 min after the injection into the nigra animals that received the small dose of ketamine. This finding provides further evidence that the substantia nigra plays an important role in opiate-induced antinociception.
Hebert
G W
GW
Department of Psychology, Louisiana State University, Baton Rouge 70803.
Baumeister
A A
AA
Nagy
M
M
D000700:Analgesics; D000758:Anesthesia; D000818:Animals; D006221:Halothane; D007267:Injections; D007649:Ketamine / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D013378:Substantia Nigra
D000700:Analgesics; D007649:Ketamine; D009020:Morphine; D006221:Halothane